1. Field of the Invention
The present invention relates to a method for erasing data from magnetic tape storage media and, more particularly, to a security-erase processing method for preventing data leakage from magnetic tape storage media in a magnetic tape library apparatus.
2. Description of the Related Art
Cartridge magnetic tapes are still used as backup recording media in a computer system. This is because cartridge magnetic tapes have a storage capacity of 400 gigabytes or larger per reel of tape and the per-bit recording cost is inexpensive compared with other types of recording media.
One method for completely erasing data from a magnetic tape storage medium is to cut the magnetic tape storage medium into pieces. However, once cut into pieces, the magnetic tape recording medium can no longer be reused. Another method is to magnetically write meaningless data over the recorded contents of the magnetic tape recording medium, but since the magnetic tape recording medium has a servo track for storing control information to control the apparatus, if the tape is magnetically erased, the control information is also erased; in this case also, the magnetic tape recording medium can no longer be reused.
A method for performing data security erase processing is known from the prior art. This method will be explained with reference to FIGS. 1 to 3.
FIG. 1 is a diagram showing tracks on a magnetic tape storage medium wound around a reel. As shown, there are a plurality of tracks 1 to n for storing data.
FIG. 2 is a diagram showing a condition in which data has been written from the beginning of track 1 to an intermediate point along track 3 on the magnetic tape storage medium shown in FIG. 1. In FIG. 2, the tracks shown in black are the tracks where data is last written, and the tracks indicated by oblique lines are the tracks filled with data written in the past but remaining unerased. The start position of the written data is recorded as a BOT (Beginning of the Tape) on the recording medium to be described later, while the end position of the written data is recorded as an EOD (End of Data) on the recording medium.
FIG. 3 is a diagram for explaining a prior art data erase method. In the prior art method shown here, to erase all data excluding the control data on all the tracks, each track has had to be overwritten with meaningless data by performing data-security erase processing. However, as the storage capacity of the media increases, nowadays it takes a few hours per reel of magnetic tape to complete this processing, which is not practical. In particular, as the processing is also performed on portions not recorded with data, the processing time increases correspondingly.
On the other hand, in some traditionally practiced data erase methods, it is decided that the data has been erased by simply writing a file mark for each track from the beginning of the magnetic tape by using backup software or the like. With such methods, however, data that follows the file mark on each track actually remains unerased, and this poses a problem from the standpoint of security.